A carboxylic acid containing a fluoroalkyl group such as ammonium perfluorooctanoate is thermally and chemically stable. The carboxylic acid can advantageously inhibit a side reaction such as a chain transfer when used in polymerization reactions, and therefore, it has been conventionally used as an emulsifier. However, there has been a problem that conditions for washing, heating and the like for removing the carboxylic acid from a resin obtained by a polymerization reaction are restricted within narrow limits.
A method of polymerizing tetrafluoroethylene (TFE) by using a tertiary perfluoroalkoxide as a surfactant in an aqueous medium, instead of using a fluorine-substituted carboxylic acid, is known as a method of producing a fluoropolymer (see Patent Document 1).
Recently disclosed as other methods of producing a fluoropolymer are a method of using a carboxylic acid having a fluoroalkyl group and an alkylene group containing 1 to 3 carbon atoms as a surfactant (see Patent Document 2), instead of a fluorine-substituted carboxylic acid, and a method of using a carboxylic acid having a fluoroalkyl group and an ether oxygen as a surfactant (see Patent Document 3), instead of a fluorine-substituted carboxylic acid.
As a surfactant which is easily removed from a resin obtained by polymerization, a material including a compound having a —(CF2O)— structure is suggested (see Patent Document 4)
Patent Document 1: Japanese Kokai Publication S61-207413
Patent Document 2: Japanese Kokai Publication H10-212261
Patent Document 3: U.S. Pat. No. 6,429,258
Patent Document 4: U.S. patent application No. 2007/0015864